2. Escal’ Atlantic

Tapping into the romance of the cruise liner era is this attraction in the submarine base that shows you the refined decor and awesome inner workings of two historic vessels: The SS Normandie, dating to 1935, and the SS France, launched in 1960. The walking tour will bring your through 20 different rooms and areas, including a dining room, piano bar and both steerage and plush cabins for passengers.

But you can also see what went on behind the scenes in the engine room and on the bridge.

Kids will be entertained by the multimedia and interactive games, while grown-ups will be wowed by more than 200 authentic artefacts from these legendary ocean liners.

3. French Submarine Espadon

Meaning “swordfish” in French, the Espadon submarine can be boarded at the Nazi U-Boat base.

The craft was launched in Le Havre in 1957 and was the first French submarine to dive beneath the Polar Ice, going as far north as 70° in the Norwegian Sea.

You’ll have an audio-guide as you explore this diesel-electric submarine, and will get plenty of insights about how the crew of 70 sailors went about their day in the eating areas, bunks and kitchens, which are almost absurdly cramped.

Sound effects on the guide will add a bit of colour, and there’s lots of science if you need the nuts and bolts.

4. Terrasse Panoramique

There’s an elevator, but you can also climb the stairway to the top of the fortified lock for a view to remember from the terrace.

From up here you can see the Penhoët dock, which at 22-hectares is one of the largest in Europe.

But perhaps even cooler is the massive “Suite de Triangles” installation by the Swiss artist Felice Varini, famed for his “perspective-localised art”. So on neighbouring docks the buildings have been covered with triangles, which only line up into a coherent work when you’re standing in exactly the right spot.

5. STX Shipyard Tour

On a two-hour drive around the STX shipyard you’ll have privileged access to a world-leading facility that employs thousands of people and uses the most sophisticated technology available.

These are the very docks that built the MS Harmony of the Seas, the largest passenger ship in the world, which completed its maiden voyage in 2016. The bus departs from the submarine base on a six-kilometre itinerary with regular stops for you to take photos or listen to in-depth explanations from your guide.

The tour takes place on Wednesdays, Saturdays and Sundays, and there’s one trip a week organised in English during July and August.

6. Airbus Tour

Also departing from the Submarine Base is the bus to tour the high-tech Airbus installation in Saint-Nazaire, setting off every Wednesday and Friday.

Because of the sensitive nature of what you’ll see you have to book your place on the tour at least 48 hours beforehand, and show ID. The Airbus site in Saint-Nazaire assembles and tests front and centre fuselage sections for every single craft made by the brand before they’re shipped by air or water to facilities in Toulouse, Spain or Germany to be completed.

It’s pretty special to see whole chunks of aircraft fuselage being “swallowed” by the gargantuan Beluga cargo planes.

10. Pont de Saint-Nazaire

From the top of the lock and submarine base you can see this epic bridge crossing the estuary.

When work was completed in 1975 this was France’s longest bridge, and it also remained the longest cable-stayed bridge in the world until 1983. Including its viaducts the total length is more than 3.3 kilometres, and the height of almost 60 metres makes it visible from a long distance.

Tour de France fans may already know the Pont de Saint-Nazaire because it has appeared on the course many times down the years, the most recent crossing taking place in 2011.

12. Jardin des Plantes

Next to the oceanfront promenade, Saint-Nazaire’s restorative botanical garden was laid out in 1880. The garden has a languid English design with footpaths bending past perfect lawns, flowerbeds and majestic trees that are both from France’s Atlantic coast and the Mediterranean.

Southern species of pines and palms flourish in this garden because of the mild temperatures and abundance of sunshine in Saint-Nazaire.

You could bring a book for an hour or two of peace, and amble down to the park’s southern boundary which gets superb ocean views.

14. Loire à Vélo

Here on the estuary it can be hard to believe you’re next to the same river that curls past those ornate châteaux in Indre-et-Loire.

But the outstanding Loire à Vélo cycle route is still here and Saint-Nazaire is the western trailhead of this 800-kilometre network.

Recently the town has done a lot to improve its infrastructure for people on two wheels, and in 2015 opened up a 10-kilometre loop that lets you visit the Submarine Base and the port or ride along the estuary for a while.

This connects with another 170 kilometres of carless trails, all on light, flat terrain although riding can get dicey on windy days.